Source : Webster's Revised Unabridged Dictionary (1913)

Hiddenite \Hid"den*ite\, n. [After W. E. Hidden.] (Min.)
   An emerald-green variety of spodumene found in North
   Carolina; lithia emerald, -- used as a gem.

Source : WordNet®

hiddenite
     n : a green transparent form of the mineral spodumene used as a
         gemstone